Description: The Emyn Duir (Dark Mountains) were a group of high hills in the north-east of the Forest, so called because dense fir-woods grew upon their slopes; but they were not yet of evil name. In later days when the shadow of Sauron spread through Greenwood the Great, and changed its name from Eryn Galen to Taur-nu-Fuin (translated Mirkwood), the Emyn Duir became a haunt of many of his most evil creatures, and were called Emyn-nu-Fuin, the Mountains of Mirkwood. [Author's note.]

Long before the War of the Alliance, Oropher, King of the Silvan Elves east of Anduin, ... had left their ancient dwellings about Amon Lanc.... Three times he had moved northwards, and at the end of the Second Age he dwelt in the western glens of the Emyn Duir, and his numerous people lived and roamed in the woods and vales westward as far as Anduin, north of the ancient Dwarf-Road (Men-i-Naugrim).

... on the day of the New Year of the Elves, Celeborn and Thranduil met in the midst of the forest; and they renamed MirkwoodEryn Lasgalen, The Wood of Greenleaves. Thranduil took all the northern region as far as the mountains that rise in the forest for his realm; and Celeborn took the southern wood below the Narrows, and named it East Lórien; all the wide forest between was given to the Beornings and the Woodmen.

The Return of the King, LoTR Appendix B, The Tale of Years: The Third Age